The present invention relates to an input/output device for an apparatus controlling industrial automatic equipment, such as a programmable auto-control or a range of such devices. The present invention also relates to a method of producing a terminal-box for such devices.
Programmable auto-controls covered by the invention comprise, in practice, a central unit and cards which have, on one edge, inner contacts for connecting them to a bus, such as a printed circuit itself connected to the central unit, and, on another edge, outer contacts intended for connection to the installation governed by the auto-control. The input/output cards contain electronic channels capable of transmitting and processing signals coming from sensors and intended for the bus, where input cards are concerned, and coming from the bus and intended for actuators, where output cards are concerned.
Each card, designated as an "input/output card" below, forms part of an input/output device also possessing a terminal-box, the purpose of which is to associate with each other contact of the card a connecting terminal for the conductors extending to the sensor or the actuators respectively.
Input circuits, each comprising in series a voltage source, a sensor switch and an electronic detection channel carried by the input card, are wired to each input device. Output circuits, each comprising in series a switch carried by the card, the actuator to be controlled and a voltage source, are wired to each output device.
In some uses, it is desirable for the circuits formed in this way to be isolated from one another. In this case, the various channels must not have any common point on the card. In other uses, it is convenient to use a card on which there is a connection giving a reference potential common to all the channels.
However, the disadvantage of this is that each type of input/output card must be produced in three forms, depending on whether the channels are isolated, the common potential is positive or the common potential is negative. In spite of this, the flexibility of use is not as it should be, since, unless production is even more varied, there is no possibility of isolating some channels while at the same time ensuring that others carried by the same card have a common reference potential. Moreover, these connections provided on the card between each channel and a common potential point are troublesome because they take up precious space on the card and often make it necessary to take special precautions to have them intersect other conductive lines of the card.
However, other problems arise when the input/output circuits are to be interconnected. In fact, it is also necessary to provide between the sensors or actuators and the electrical source or sources one or more auxiliary terminal-boxes which are costly and bulky and which make the installation more complicated.